1. Field of the Invention
The present invention relates to electric power generators and more particularly to electric power generators for use in a downhole drilling environment.
2. Background
The ability to access and transmit data along a drill string has been a goal of the oil and gas industry for more than half a century. As exploration and drilling technology has improved, this goal has become more important to the industry. For example, to take advantage of various advances in downhole tools and techniques, it would be highly beneficial to transmit real-time data such as temperature, pressure, inclination, salinity, and the like to the surface where it can be analyzed and used beneficially. Nevertheless, because of the complexity, expense, and unreliability of many proposed or attempted downhole transmission systems, these systems have failed to achieve significant commercial use or acceptance.
In U.S. Pat. No. 6,670,880 as well as numerous other related patents and pending patent applications, the present inventors have disclosed a “downhole transmission system” that overcomes many of the problems and limitations of prior art systems. In this downhole transmission system, data is transmitted in real time along a drill string using network hardware integrated directly into the drill string. This network hardware enables high-speed communication between surface equipment, such as analysis, diagnostic, and control equipment, and downhole equipment, such as tools and sensors located along the drill string.
With the installation of network and other related hardware comes the need for an efficient and reliable power source to operate this hardware. Such a power source must be able to provide reliable power in the extreme conditions of a downhole environment. Although batteries provide one option, the use of batteries is hindered by their inherently finite life and the need for frequent replacement and/or recharging. This may be problematic in downhole drilling application where access to these batteries may require tripping and disassembly of the drill string. Battery function may also be impaired by the extreme temperatures, pressures, or other conditions downhole.
In addition, various electrical generators have also been disclosed for generating electrical power in a downhole environment. These generators, however, create additional problems that limit their usefulness downhole. Specifically, some of these generators obstruct the central borehole of the drill string. This undesirably inhibits the flow of drilling fluid and obstructs the passage of wireline tools or other equipment through the central bore. Moreover, many downhole generators are designed for implementation in production wells rather than in downhole drilling strings. Some of these generators may also be complex and have substantial mass, making them costly to implement and maintain and/or difficult to replace or repair. In other cases, these generators may be ill-equipped for operation in the extreme temperatures, pressures, and corrosive conditions downhole.
Accordingly, what is needed is an improved and robust electrical generator for use in a downhole environment. Ideally, such a generator would generate electricity without obstructing the central borehole of a drill string. Further needed is a generator that is more compact and efficient than previously disclosed downhole generators.